Mechanical warewashing machines have been common in the institutional and household environments for many years. Such automatic warewashing machines clean dishes using two or more cycles which can include initially a wash cycle followed by a rinse cycle. Such automatic warewashing machines can also utilize soak cycle, pre-wash cycle, scrape cycle, second wash cycle, rinse cycle, a sanitizing cycle, and drying cycle. Any of these cycles can be repeated, if desired, and additional cycles can be used. Rinse agents are conventionally used in warewashing applications to promote drying and to prevent the formation of spots. Even when both goals are accomplished, water solids filming is often evident. After a wash, rinse, and dry cycle, dishware, cups, glasses, etc., can exhibit filming that arises from the dissolved mineral salts common to all water supplies. Water solids filming is aesthetically unacceptable in most consumer and institutional environments.
Water solids filming on cookware, dishware and flatware is a particular problem in the presence of high solids containing water. In general, rinse waters containing in excess of 200 ppm total dissolved solids (TDS) tends to leave a visible film on glass and flatware after they are dried. Above 400 ppm, the films become objectionable, and above 800 ppm, the films are particularly aesthetically unacceptable. The TDS content can be reduced by a demineralization process, such as reverse osmosis, which can be expensive.
In order to reduce the formation of spotting, rinse agents have commonly been added to water to form an aqueous rinse that is sprayed on the dishware after cleaning is complete. The precise mechanism through which rinse agents work is not established. One theory holds that the surfactant in the rinse agent is absorbed on the surface at temperatures at or above its cloud point, and thereby reduces the solid-liquid interfacial energy and contact angle. This leads to the formation of a continuous sheet which drains evenly from the surface and minimizes the formation of spots. Generally, high foaming surfactants have cloud points above the temperature of the rinse water, and, according to this theory, would not promote sheet formation, thereby resulting in spots. Moreover, high foaming materials are known to interfere with the operation of warewashing machines. Common rinse aid formulations used in warewashing machines are used in an amount of less than about 1,000 parts, commonly 10 to 200 parts per million of active materials in the aqueous rinse. Rinse agents available in the consumer and institutional markets include liquid or solid forms that are typically added to, dispersed or dissolved in water to form an aqueous rinse. Such dissolution can occur from a rinse agent installed onto the dish rack. The rinse agent can be diluted and dispensed from a dispenser mounted on or in the machine or from a separate dispenser that is mounted separately but cooperatively with the dish machine.
Many commercial rinse agents include polyalkylene oxide copolymers and ethylene oxide/propylene oxide block copolymers. In such materials, the ethylene oxide block tends to be hydrophilic while the propylene oxide blocks tend to be hydrophobic producing a separation of hydrophilic and hydrophobic groups on the surfactant molecule. Surfactants can be formed by reacting an alcohol, a glycol, a carboxylic acid, an amine or a substituted phenol with various proportions and combinations of ethylene oxide and propylene oxide to form both random and block copolymers.
Exemplary rinse agent compositions are described by U.S. Pat. Nos. 5,589,099 to Baum; 5,447,648 to Steindorf; 5,739,099 to Welch et al.; 5,712,244 to Addison et al.; 5,545,352 to Pike; 5,273,677 to Arif; and 5,516,452 to Welch et al.